Hydraulic driving means for winding and rolling machines



Oct. 13, l953 A. SPENCER ETAL HYDRAULIC DRIVING MEANS FOR WINDING ANDROLLING MACHINES 3 Sheets-Sheet l Filed March 3, 1948 mO-A I /NVENTUQARTHUR sPENc'R um Oct. 13, 1953 A SPENCER ETAL 2,655,06()

HYDRAULIC DRIVING MEANS FOR WINDING AND ROLLING MACHINES Filed March 3,1948 5 Sheets-Sheet 2 Oct. 13, 1953 A. SPENCER ET AL 2,655,060

HYDRAULIC DRIVING MEANS FOR WINDING AND ROLLING MACHINES Filed March 5,1948 5 Sheets-Sheet 3 FIGB.

ARTHUR x ENMWJW' E W17 Wi w AGENTS Patented Oct. 13, 1953 HYDRAULICDRIVING MEANS FOR VVINDING AND ROLLING MACHINES Arthur Spencer and JohnHewitt, London, England, assignors to Vickers-Armstrongs Limited,London, England, a British company Application March 3, 1948, Serial No.12,848 In Great Britain March 19, 1947 4 Claims.

This invention relates to hydraulic rolling machines for rolling metaland metal alloy strips or stock by feeding the material between rollsfrom one drum to another, the material being drawn between the rolls ofthe mill when passing from one drum to the other, so that in onedirection of operation one of the said drums acts as a coller-on drumand the other as a'coilingoff drum. An object of the present inventionis to provide a reversible mill for rolling metal strips or stock havinga hydraulic pump serving a motor for each drum and providing independenthydraulic drive therefor so that it is possible to operate any singledrive to facilitate threading in of the work.

Another object of the present invention is to ensure maintenance of theoperative pressure across each pump and motor and the compensation forchanges in diameter of the coil buildup to be made by adjusting thehydraulic unit.

Another object of the present invention is to provide a mill in whichthe pressure on the work is governed by a servo unit and thereby obviatethe disadvantages of relying upon lease Valves for this purpose.

Another object of the present invention is to provide in conjunctionwith a reversible hydraulic rolling mill means which responds accuratelyto a signal from the pressure side across each pump and associated motorto correct the strokes iof the motors to maintain in such motors aconstant pressure and in which the said means has a derivative controlwhich reduces any tendency for the hydraulic pressure to surge f andfurther acts on the strokes ofithe motors stroke of the i pressure rey ytratmg embodiments thereof, and wherein:

strip adjusts itself automatically to the process by reason of the factthat the torque cannot be applied until there is a re-action of theprocess.

VA still further object of the present invention is to provide areversible rolling mill in which,

in addition to the means driving the rolls there drums can act as a`(miler-,011 andthe other as r to said drum and to maintain asubstantially constant horse power in the motor driving said drum.

In addition to the foregoing, an object of the present invention is tocontrol the stroke of the hydraulic motors positively by a pair ofhydraulic fluid pressure actuated drivers having a source of operativefluid pressure distinct from that in the closed circuits of the pumpsand motors. That is to say, there is a positive duid pressure actuationof the drivers varying the strokes of the motors both for increasing anddecreasing the strokes of the motors.

In orderA that the invention may be clearly understood and readilycarried into effect diagrammatic drawings are appended hereto illuslFigure 1 is a diagrammatic view showing a mill with three hydraulicdrives to (a) rolls, (b) coiling-oif drum, (c) culling-on drum. Eachdrive consists of a hydraulic pump and motor the hydraulicpumps beingdriven by electric motors or any other prime movers. This gure alsoshows a` modified method of obtaining the desired correction for changein tension in the strip when a highly sensitive response to change isnecessary. 4 Figure 2 is a diagrammatic view showing the completehydraulic circuits of one arrangement of control unit for obtaining thecontrol of the hydraulic motor horse power in the coiling drums.

Figures Band 4 are detail views showing a modification of the phaseadvance or error-derivative part of the appliance.

Referringto Figure 1 of the -drawings showing a milljoperat-ed vbyhydraulics. there are shown three hydraulic drives each hydraulic systemconsists of a variable stroke pump feeding a hydraulic motor. In thiscase the three hydraulic pumps as shown are driven by two electricmotors, one motor |00 driving the pump for the main mill drive and theother motor H3 fitted with shaft extensions at both ends driving the twopumps operating the coiling on and coiling off drives, but may be drivenby a single motor through gears or by any other'form of prime mover.

The pump for the roll drive has a variable stroke and controls the speedof the hydraulic motor |02 which has a fixed stroke. The coiling drumpumps |03 and |03 also have variable stroke, these are coupled togetherwith the stroke of the milll pump |0| through shafts and gears |04, |05,|06 and |01 to handwheel |08 so that the delivery of all three pumpshave the same ratio at all speeds of the mill. The hydraulic motors |09and |09' for. both-fthe. drums ||0 and ||0 have variable stroke. Thestrokes of the hydraulic motors |09 and |09 are positioned by controlunits ||0a; andi- M205 through linkages |20, |2|, |22 and i233 or IH",|20, |2|', |22', |23. Assume the strip oro-thermaterial being dealt withis passing from; leitiftoright of the mill as depicted in Fig.. 1'.Drum.V ||0 coiling ofi and drum ||0' is coiling-on. When rolling heavygauge metal and under like conditions in which there is not likely to beany appreciable change in the high pressures required to operate thevmotors |09! and' |08 orl in which the change in such pressures willV notproduce any greatl change in the: eiiect; in the; heavy gauge metal, thecontroI-units Hita and ||0b aret connected to the pressurei systemthrough pipes ||2 and |12". However, when dealing with quite thin gaugemetal strip,V e.. gf. of a foil-like natu-re, and other materials whichare very susceptibley to change in tensioni. it is desirable to connecttheV control units: ||0 and ||0b to a constant pressure source whichfeeds the units at pressures controlledby the tension in the material,as hereinafter describedf with. reference to the devices A and? I3` ofligure. l, The pipes connected to the units H0@ and'. Hb.- in this caseare indicated at |'|2a and H22. Handwheels ||3 and H3" are for settingtheA spring which will determine the operating pressure in the pipes ||4and'r |I`||'l between the hydraulic pumps |03 and |03 and hydraulicmotors |09 and |09. The pipes IM, I-M, H5', H15", ||6 and IIB connectthe hydraulic pumps (0|, |03 and |03 to the hydraulic motors |02, |09and |09'.

The foregoing describes the arrangement of a reversing mill where eachcoiling drum reverses its operation, i. e. from of coiling to on coilingor on coiling to off coiling according to the direction of the strippassing through the rolls The horse power input to coiling motors |09and |09 will depend upon the speed of the strip and the tension in thestrip which is equivalent to the quantity of fluid and pressurecirculating through the motors |09 and |09. Therefore since the quantityof iluid can be made to vary as the strip speed, by virtue of the factthat the handwheel |08 controls simultaneously the stroke mechanism ofthe three pumps |0|, |03 and 03', a control of pressure in the coilingmotor system will give a control of tension in the strip.

The control units ||0u and ||0b are-designed to give a constant pressurein the pipes ||4 and ||4 feeding the motors |09 and |09.vsee descriptionof Figure 2. When the pressure in the coiling-on motor |09 risesV due-to thej increase of coil diameter, the control 0b'w ill move lever toincreas the stroke of thermo,- tor |09' and give out a greater torque ata slower speed, until the pressure has been restored to the predetrminedsetting to suit the required tension.

Meanwhile, the coiling-off control unit ||0u i operates in the oppositedirection. The coilingoff drum ||0 has to give a resistance to thev pullof the rolls and for this drive the hy-v draulic motor |09 is beingdriven by the rolls' via the strip and drum ||0. Therefore part of thepower is regenerated back into the electric motor IH' as the,'hydraulic4 motor |09 is acting as a pump and the hydraulic pump |03 isacting as a xed stroke motor. When the drum diameter is reduced by theuncoiling of the. strip., the. pressure .in pipe ||4 tends to increase,because owing to the increase in speed the motor |09 is delivering agreater quantity of iluid thanv thatI corresponding to the capacity andspeed of pump |03 and in this case control unit ||0ay will decrease thestroke of motor |09 scrthatv the; pressure is maintained at the higherdrumspeeds It will be seen that the control ||0a operates inareversedirection when uncoiling, i. e. the pressure increase, in this case inpipe ||4, tends to, decrease-the stroke. The aforesaid couplingsbetwecnthe control', umts 10a and H012 have reversing linkages with theappropriate mo.- tors operated byfhandlevers; Il!! and; H9! which4 haveto be.L changed, at; the end of the. pass for the next. pass; toi be.taken in the reverse; direction. For example... the hand leverv H9' bymoving frame |20 determines. whether control unit shaft. |24 movesstroke.' lever in clockwise or anti-clockwise direction e. the posi-tionofj the block |23 Iirli the' slot Off trame |20 determines whether the:pulir-push movement, 0f the control box shaft |21' is; operating throughlink |22 or |12| to. top or bottom of; lever It will be obvious that theabove considerations apply' whelemateril, Such. aS Strip Q1? Wire isbeingv pulled through rolls'v or dies by the coiling on drum from thecoiling ofi` drum Without an intermediate. drive.. In such a case thewholel power is. provided by the coiling on. drive the coiling off driveproviding back tension as required.V The apparatus employed is the sameas that describedv and depicted in Figure 1 with the deletion of maindrive Dump |0| and hydraulic motor |102.

Referring to Figure. 2 ofthe drawings the aforesaid hydraulic. powerunit can be regarded as the; hydraulic. motor |09" aforesaid in whichthe stroke of the. pistons operating in the cylinders is adjusted bycontrolling theA lever ofthe stroke control or tilting member from thecontrol unit ||0b which embodies servo means responsive to differencesin tension and/or rate of travel of the material from the supply sourceto the take-up means, the hydraulic motor being connected to a pump'l03driven at. a pre,-l determined speed. The motor |09' is preferae bly ofthe swash plate type.

The servo device aforesaid embodies a sliding type of pilot valve toperated olf a system or linkage and controlling the admission ofpressure fluid to a cylinder 5 accommodating a piston S having aypush-pull connection |24 to the actuating lever of the tilting plate ofthe motor |09' the piston rod 8 extending through both ends of thecylinder, the end remote from the motor sliding in a cylindrical chamber9 acting as a dash-pot device and accommodating midway between its endsa needle type bleed valve I0 together with means (hereinafter described)for ladjusting the reaction of the dash-pot to the 'movement of thepiston, the arrangement being 'such that when the piston 0 is moved toadjust vthe tilt of the plate of the motor |09 suction or '-P1'05ureaccording to the direction of movement of the piston 6 is created in thedash-pot 9, and the piston I I of the dash-pot is moved against theinfluence of a leaf spring l2 further into or away from the cylinder,the dash-pot piston being connected by a link I 3a 4to the leaf springI2, which link is connected about midway between its ends to one end ofa relatively perpendicular lever I4, e. g. as shown, its upper end,which by reason of the traction of the dash-pot piston, applies throughthe medium of a connecting rod I5, sliding movement to the pilot valve.The lower end of this lever I4 turns about the upper end of a furtherlever I6 controlled through the medium of a rod I1 from a iiexiblediaphragm I8 supported at its perimeter in a pocket I9 in such mannerthat variations in pressure in the pocket will produce a movement of theaforesaid rod I'I and consequently adjustment of the lever I6 by reasonof the pivotal connection I5' of the rod I'I to the lever I5. The leverI6 actuated olf the diaphragm can, for the purpose of designation beregarded as the diaphragm actuated lever, the rst mentioned lever whichis connected to the pilot valve being suitably designated as thedash-pot actuated lever.

The diaphragm I8 with its pocket I9 forms part of a stabilising devicecomprising an outer housing or block 29 within which slides acylindrical inner block 2| having a quite restricted movement relativelyto the outer block and being damped by a dash-pot 22 in one end of theouter block, the piston 23 of this dash-pot being formed cn the end of arod 24 remote from the inner block and carrying between its ends adoublepiston type of valve 25 operating in a chamber 25 fed by a conduit26 leading from the aforesaid pocket I9 and having a port 2'I toexhaust, this pocket I9 also communicating with a bore 28 in the end ofthe aforesaid outer block remote from the end containing the dash-pot,this bore receiving a double-piston type of valve 29 connected by a rod39 and link 39' to the upper end of a further lever 3l the fulcrum 32 ofwhich is midway between its ends, the lower end of this third leverbeing connected by a link 33 to an abutment member 34 `of a spring 35 ofa pressure measuring device, comprising the plunger 36 carried by theabutment 34 and operating within a cylinder 3l, which when rolling heavygauge metal as mentioned hereinbefore, can be connected by a conduit II2 to the feed line I I4 from the pump HB3 to the motor H39.

However, when winding or rolling the thin gauge materials, such as metalfoil, or even plastic materials having a relatively high yield totension in which relatively low pressures are employed it is necessaryto connect the conduit I I2 to a source of pressure independent of thefeed line IM', and in which the pressure applied to the cylinder 3'! iscontrolled from the tension of the material being wound on to or offfrom the drum H9. Hence, in Figure l there is shown at A and B iioatingbearings 80 and 89' for the drums II9 and lili', each bearing beingfixed to a plunger 8l operating in a cylinder 82 to which is connected apipe 83 connected to the pressure side of a constant capacity pump (notshown). rlhe pressure from this pump is fed into the cylinder 3l vialine IIZb (or Ila) and as the tension in the drum H9 builds up againstthe -pressure in the cylinder 82 a release port 84 leading iby line 95to a tank in the circuit of the latter mentioned pump is graduallythrottled down, and the resulting pressure obtained by this throttlingdown is fed into line II2b to the cylinder 31 and the tilt of the leverIII' thereby constantly adjusted to take care of any tendency for thetension in the material to change.

The said bore 23 accommodating the latter mentioned d-ouble piston typeof valve 29 communicates with the inlet 4 of the cylinder 4a of theaforesaid pilot valve via a pipe line 49 leading from the discharge 4 Iof a gear pump 4I (driven from an electric motor 42) and a branch line49a. This motor 42 would normally be a fractional horsepower motor.

An adjusting screw 58 is provided to enable the loading of the spring 35to be varied, the screw 5B being operated via worm gear 59 driven from atension adjustment shaft 59, and the aforesaid spring 35 is interposedbetween the said abutment 34 and one end of a housing 43 and connectedby suitable remote control means, e. g. a cam or link and lever 44 andshaft 45, to a tension indicator 46 to indicate the pre-setting load onthe spring. The shaft 42 on the aforesaid low horsepower electric motor42 to the gear pump 4I has a gear connection 42a to a shaft 41 drivingan eccentric 48 operating a longitudinal rod 49, the end of which remotefrom the eccentric is connected to the lower end lof a link 59 pivotedat its upper end to a fixed pivotal point 5I thus providing a dithermechanism to keep the whole of the mechanism of the control apparatusalive and thus remove static friction. This ensures that the pilot Valve4 will accurately return to its closed position when no pressure errorexists, and will thereby eliminate any tendency for the tilt controlpiston 6 to creep due to the pressure iiuid .being admitted through thepilot valve 4 to one side of the tilt control cylinder 5. This dither onthe pilot valve also enables the control to respond to very smallsustained variations in pressure in the pump and motor circuit.Alternately, this dither may be effected hydraulically by introducingpulsations into the chamber 9.

To enable the pilot valve 4 to be centered accuH rately in its valveblock when the links 3 I, I6 and I4 are in the neutral position the leafspring I2 is xed to a short cranked extension 6 I of a lever .6Ioperated off an adjuster screw 62.

The position of the fulcrum 32 of the third mentioned, or lower endlever 3l i. e, of the lever connected to the abutment of the spring 35of the pressure measuring device, is adjustable so that the movement ofthe pilot valve l for a given Variation in pressure due to the loadreaction to the hydraulic motor |09' circuit can be varied on test toascertain the most suitable rate of response of angle of the lever Ill',i. e. of tilt. In this connection such fulcrum, which as aforesaid isbetween the ends of this lever, is connected by a bracket 34 and apush-pull rod 32a to a remote control adjuster 52, this adjuster therebyadjusting the position of the fulcrum 32 of the lever 3| which connectsthe piston 35 to the aforesaid stabilising device.

The aforesaid double piston type of valve 29 of the stabilising devicehas its rod 33 prolonged into the inner or sliding block of thestabilising device to carry at its end remote from the double pistontype valve a further similar type of valve 53. In operation theaforesaid gear pump et supplies the bores 28 and 25 of the two doublepiston type valves 29 and 25 respectively with fluid at a constantpressure, the fluid passing through the rst mentioned double pistonvalve bore 28 and a port I9 leading to the pocket Iii containing thediaphragm I8, from whence it passes via 'the .conduit 26 to the bore 25of the outer block of the stabilising device and from whence the fluidpasses via outlet `21 to exhaust.

The double piston valve 29 connected to the upper end of the lower lever3| of the first mentioned three levers and the double piston valve 53 inthe sliding block are pre-set so that when the said three levers I4, Sand 3| are in the neutral position the port I9 communicating with thesaid pocket I9 and the outlet port 21 in the outer block of thestabilising device are of the same area and half open as shown,consequently the pressure drop through each is the same. By this meansthe diaphragm in the pocket is initially deflected under a pressure ofhalf the supply pressure.

Any movement of the aforesaid double piston type of valve 29 connectedto the levers i6 and 3i changes the `area of the port I9 leading to thepocket and at the same time opens two ports 54 and 55 in, andcommunicating with, opposite ends of a chamber 55 receiving the slidingblock 2|, these two ports being otherwise covered by the piston elementsof the double piston valve in the sliding block as shown. The opening ofeither one of these two ports 54, 55 allows pressure fluid to act on theend of the sliding block coinmunieating with the appropriate port, sothat the block will then move in the same direction of movement as thevalve until the two ports 51E, 55 are closed and the outlet 21 in theouter block is the same area as the port I9 communicating with thediaphragm pocket I6. Owing to the aforesaid dash-pot 22 in one end ofthe outer block controlling the speed of movement of the double pistonvalve piston controlling the said exhaust 21, there is a time lagbetween the changing of the area of the port I9' communi eating with thepocket |9and the equating of the areas of this latter port I9 and thesaid outlet port 21. This time lag can be adjusted by means of adash-pot adjuster comprising a screw actuated conical valve 51establishing communication between the dash-pot 22 and a source ofsupply of fluid.

The foregoing describes the general arrangement of the control gear, andit will be appreciated that in operation when, e. g. as aforesaid, theapparatus is adapted to the winding, rolling or feeding of materialswhich are very susceptible i to the influence of changes in tension,having regard to the fact that the variable rate spring takes care ofchanges in tension build-up in the strip material, i. e. changes in loadon the means driven by the hydraulic motor |59 (or |59), by respondingto such changes so as to vary the setting of the lever III', theeffective horsepower input to the hydraulic motor |69 is maintained at apredetermined value depending upon the tension required in the materialand its velocity, e. g. in the feeding of strip metal from rolls to atake-up drum.

To maintain the said pressure constant, any error in pressure is asalready described, utilised to move the tilt of the plate of the motor|69 in such a direction as will restore the pressure to itspredetermined value. The control comes into the category of a rstderivative of error control, i. e. the movement of said pilot Valve 1controlling the admission of pressure fluid to the cylinder 5, isproportional to the error plus a function of the rate of changes oferror. For

example, Ylet the error in the pressure be P then the input to the pilotvalve will be K( f (P) -I'- =pressure error:

rate of change of pressure error The rst portion of this expression isobtained by means of the pressure measuring device 36 which is setbefore starting to roll the strip, by means of the tension adjustmentshaft 60, so that when the tension in the strip is set at the requiredvalue, the pressure in the pump and motor system balance 'against thesaid spring 35 whereby the said three levers I4, I6 and 3| are held inthe in-line or neutral position, the pilot valve 4 is closed, and thereis no movement of the tilt control piston 6. Any variation in thistension produces a variation in strip horsepower and in pressure in themotor circuit and consequently the said three levers move from theneutral position, the pilot valve 4 opens, and the tilt control piston 6moves to adjust the speed of the motor. Variable rate springs can beused in order that a giveni variation in pressure between the pump and`motor produces the maximum rate of change of the speed of the hydraulicmotor and its associated drum.

The -second portion of the expression fldt is obtained from theaforesaid stabilising device. It is assumed that the double `pistonvalves 25 and 53 in the said bore of the outer block 20 and in thesliding block 2| are suddenly moved in the direction of the arrow A,there is a sudden reduction of the area of the port I9 leading to thediaphragm pocket I9, whereas the adjustment of the area of the saidoutlet port 21 is retarded. This will cause a greater pressure dropthrough the port I9 than through the outlet port 21, with a consequentreduction in pressure in the said pocket I9, and hence the diaphragmwill push out the rod I1 connecting it to the intermediate one I6 of thethree levers.

A reversal of the movement of piston valves 28 and 53 will result inthis rod I1 and lever I6 being pulled in.

This displacement of the rod I1 is proportional to the rate of change oferror, since the pressure drop in the pocket is proportional to thedifference in area of the pocket port I9 and outlet port 21 and theslower the movement of the double piston valve 2B the closer the doublepiston valve 25 connected to the sliding block 2| follows the valve 29,and the area of opening the said exhaust port 21 follows the area ofopening of the port I9 connecting with the pocket I9. Variations inresponse of the sliding block can be effected by adjustment of the valveArising out of the foregoing, as the area of the outlet port 21approaches the area of the diaphragm pocket port I9', the pressure dropthrough the exhaust port 21 approaches the pressure through thediaphragm pocket I9 and. consequently the displacement of the rod I1connected to the diaphragm is gradually reduced until the area of theoutlet port 21 equals the area of the diaphragm pocket port I9 whencethe diaphragm is returned to its initial position.

Now assume that there is a rise in tension in the strip above thepredetermined value. This will create a rise in pressure in the conduitII2 (or I|2b) and the resultant movement of the piston 36 in thepressure measuring device will be in a direction of the arrow B, thelever 3l turning about its fulcrum 32 and the coupled double pistonvalves 29, 53 of the stabilising device will move inwards. Theintermediate lever l 6 of the said three levers will consequently turnabout the pivot I6 on the rod connected to the diaphragm, and the lowerend pivot I4 of the upper lever I4 will move out. At the same time thediaphragm rod Il will move out owing to a reduction of pressure in thesaid pocket as previously indicated, the intermediate lever i6 willpivot about its lower end lBa and its movement will be increased. Thislatter additional movement due to the movement of the diaphragm rod ilis gradually removed as indicated in the preceding paragraph. 'I'heupper lever I4 of the three leversI will pivot about its upper end |4aand the pilot valve I4 will open in the direction of the arrow C.Pressure iiuid will then be admitted behind the tilt control piston 6and the tilt of the motor plate will be increased and the speed of thewinding drum reduced.

When the tilt control piston 6 moves, it will create a suction in itsassociated dash-pot 9, and the piston l l therein acting against theleafspring i2, will be drawn further into the cylinder. The upper leverI4 will pivot about its lower end and the pilot valve 4 will begin toclose. The suction created in this dash-pot 9 will draw fluid throughthe adjustable needle valve lil of the dash-pot, and opposing the leafspring l2 tends to close the valve 4 so that when the pressure in themain system is restored the rate of the piston 6 has been retarded andapproaches its new position simultaneously with the restoration of thepressure in the system. This action is continuous While the tilt controlpiston d is moving, and tends to restrict the rate of change of tilt oracceleration of the drum, smoothing the operation of the control andreducing any tendency for the tilt lever lll to overshoot the requiredposition. The amount of restriction to the rate of change of tilt togive the most stable condition is obtained by means of the dash-potadjuster l0.

If the pressure in the pump-motor circuit falls, a reversal of the abovesequence of events takes place, until the pressure returns to the normalvalue and the said three coupled levers are again in their neutralpositions.

When it is desired to regulate the take-up of the fed material insynchronism with the processing of the material in such manner that ifthe feed or processing stops, the material can be fed over or through afeeler in the form of a lever, and for a photo-electric cell device orother means for measuring catenary, and the lever, or its equivalentconnected through the medium of a mechanical, hydraulic or electriclinkage, so that the rise and fall of the lever, or the effect of thechange of catenary, i. e. the displacement of the strip materialrelatively to the light source of a photo-electric cell is transmittedto the lever 3| instead of to the cylinder 3l and spring 35 to obtain acontrol of the hydraulic drive.

In the embodiment shown in Figure 3 the lever 3l is connected at itsupper end to a piston 29h so that this piston moves at a velocityproportional to the rate of change of error, resulting in oil beingpressed out of or drawn in via the adjustable orice 'I0 giving apressure in the port lli depending upon the rate of displacement of thepiston 29h and adjustment of area of the orice lil, which pressurereacts on piston I8b in cylinder 12 against the appropriate one of a 10pair of balanced springs 'H giving a movement to the rod ilproportionate to this pressure. Thus the displacement of the piston I8band lever point IB therefore depend upon the velocity of the piston 29h.The broken line parts (Fig. 4) show the effect on the lever assembly, aterm being added into the system. The addition of this term, or thisadditive motion has a damping eiect on the system.

The foregoing stabilising means is an appreciably simplified alternativeto the stabilising means Ypreviously described, the unit being submergedin oil, so that when the error signal has a velocity to the right in thediagram oil is sucked into the cylinder 'I3 and the piston |819 moves tothe left. By providing an adjustable orice l0 the ratio between thedeflection of the piston |82: and the velocity of the piston 29h can beregulated.

It will be appreciated that the present invention is applicable also tothe automatic control in quantity output of a pump so as to obtain auniform pressure in lines to a number of apparatus fed by the pump, andin which the number of apparatus in use at a time is subject tovariations e. g. in a works or aircraft where one pump is common to aplurality of hydraulic duid pressure actuated apparatus. In such an arnrangement changes in the number of apparatus being fed by the pump willchange the pressure in the pump discharge side unless provision is madeto adjust, e. g. the stroke and consequently quantity output of the pumpautomatically according to the changes in reaction due to increase ordecrease in number of apparatus being served. Hence, by controlling thepressure in the line 38 to the cylinder 3l via means responding to thereaction in the supply line from the pump, the necessary changes inquantity of iiuid flowing per given unit of time from the pump can beeiected so as to obtain constant pressure to the apparatus in use.

We claim:

l. A reversible rolling mill, comprising rolls for rolling the material,a power unit driving the rolls, a pair of hydraulic pumps, a prime moverdriving said pumps, and a pair of variable stroke hydraulic motors, aclosed hydraulic circuit across each pump and its associated motor inthe form of a supply conduit and a return conduit across each pump andits associated motor, a pair of drums one driven by one of said motorsand the other by the remaining motor, said drums each servingalternately to coil-oil and coil-on the material being rolled, so thatas one acts as a coiler-on, the other acts as a coller-off and viceversa and the coiler-off drum transmits the tension in the materialacross it and the rolls to its motor to feed back part of the powergenerated to the said prime mover, means to change the direction ofdrive to said drums to reverse the direction of feed of the materialbetween the rolls, iiuid pressure actuated means to increase the strokeof the coiling-on drum motor as the coil diameter increases so as toincrease the torque applied to said drum and to maintain a substantiallyconstant horsepower in the motor driving said drum, a pair of hydrauliciluid pressure actuated drivers having a source of operau tive fluidpressure distinct from that in the aforesaid pump-motor circuits andconnected to the stroke varying means of the two motors to posi-n tivelyactuate the stroke varying means both for increasing and decreasing themotor stroke, a v alye with each -saidf -driver controlling lthe flowOfznplessure Huid tositsassoeiateddriver both as I'Qgalfdiireton andaeiective pressure, `means receiving a controlling.- signal Y from'- lthey supply conduit, of eachl pumpw-andmotor regulating the position ofeach said valve to control the direction and extent of displacement ofeach said driver so as to give a mo'tor stroke changing response to the`reaction ee'ct inthehydrauliccir cuite of the :assooiatedzpump andmotor due to the change in tension in .the materialilbeing?*fed` throughthe roilsndrthfe changein build-up of thematerial-being woundfon theceiling-up drum and the'reduc'tion finmaterial being coiled-offthe05h61'drum?` if. :1:: 311.. :5, it; r

, 2. Arolling mill according to claim 1 including in addition a`pumrrfee'dingza motor( driving thev rolls, thezmotordrivingthe rollingmeans havinganormally `ixed stroke, and I"means common td all of saidpumps tc"y adjust the pumps so that at least the two pumps driving thetwo drum motors l canfhavezthefsame hydraulicfoutput,` and the due` tothe'reajction of the strip material, servo Y means; receivinganoperating` signal from said 12 latter means and adapted to control theextentv o'f 'displacement of"'said'vellve to Vcon'iplete theconnectioribf thesaid cylinder to the' source of hydraulic fflu'd'pressure and thereby to maintain a substantially @constant 'horsepower'output o'fV the associated"motor` du'e to the adjustment of the strokecontroller, and 'a fluid pressure 'd-is'placedflm'emberoperatively'connected to the valve andfrespon'di'ngtomate of.' change ofthe load on` themotor jto introduce a compensatingmove; m'ent into'th said-valve means'.

"4;*1'Alrolling mill' accoding'to claim l wherein sadm'eans'adapted'to"b"e pre-set to respond 'toa predetermined *load on" the motoris"`a"spring leaded' member displace'able"against'the in'ueiice off its-spring 'by 'the "influence ofhydraulic pres? sure infin-efsupply4side-er the associated meter.'

JOHN Hnwrr'r."

References Cited in theA fileY of this patent PATENTS..

